A conventional VDL (Variable Delay Line: a variable delay circuit) has a plurality of delay paths that are different in the amount of delay. Since the conventional VDL does not have a mechanism to determine the amount of delay, the appropriate delay path has been selected in accordance with the amount of delay at the time of designing to determine the amount of delay.
Incidentally, a widely known relevant technology is a phase adjustment circuit that can adjust the difference in phase of two pulse signals so that there is substantially a phase difference of 180 degrees between the pulse signals even if there is variation in the amount of delay of the individual inverters that constitute the variable delay circuit. [Patent Document 1] Japanese Laid-Open Patent Publication No. 2000-315941
However, the conventional VDL may not be able to ensure the accuracy and range of adjusting the amount of delay to be suitable for the frequency of external input signals. Moreover, the conventional VDL cannot take into account manufacturing variation, temperatures inside chips and a drop in voltage of a power supply when adjusting the amount of delay.